Looking for opinions here. First I understand the benefit of single parity is to withstand a single drive failure (two parity = 2 drive failures) and allow the system to continue running.

 

I am a home user with a relatively small server, not business critical. All important files are backed up to a secondary unraid box, and all critical files are backed up there, to another external hard drive in my house, and to a cloud backup service. I'm well covered for everything that actually matters. The stuff that doesn't matter (mostly plex related stuff) I can get again over time, and if it's all gone, so be it. 

 

The cost to maintain single parity is the price of a 10TB drive, which if not used for parity would allow a larger backup server capacity, or a large main server capacity. Parity has been un-needed in the 5 years I've had an unraid box, and now that I've had two drives become invalid together, it also didn't matter that I had a parity drive. So this has caused me to think about it - what actually is the point of parity for a small home server with proper nightly backup routines in place?

 

Thoughts?

 

Tiwing.

I think it really depends on :

• what type of data you store
• how much of it is actually backed up
• how bad it would be to miss the parts not backed up
• how hard/easy it would be to get it back

Then you make the decision that is the best for your use case. 0 / 1 / 2 parity drive(s).

For me it’s ease of replacement. I have 1 Parity and 8 data drives. If a drive goes down I simply replace the drive and hit rebuild. No worrying about copying data around or where are my files so I can put them back. 
 

Also not only because of failure, but because of upgrading. In the days of 2TB being largest and now 12TB being very common it makes upgrading drives easier. Take out a smaller drive and then hit rebuild. Done. 😃

6 hours ago, tiwing said:

what actually is the point of parity for a small home server

What @kizer said sums it up for me.  I also backup everything to a second server and to external hard drives (in addition to the cloud).  However, when it comes to replacing or upgrading a drive, it is a far easier process because of parity. 

 

Unless you are backing up drive by drive (instead of by shares), you will have to figure out what is missing from the failed drive or what belongs on the larger replacement drive rather than parity doing it for you.

Yeah that makes a huge huge amount of sense, and I do back up by share. What great thoughts and thank you. For me, that sums it up... Well worth the decrease in headaches to have parity drive sitting there should something go sideways. Cheers! 

43 minutes ago, Hoopster said:

Unless you are backing up drive by drive (instead of by shares), you will have to figure out what is missing from the failed drive or what belongs on the larger replacement drive rather than parity doing it for you.

My important stuff is in 2 user shares and will fit on 2TB. I have several externals that size which I rotate and store off-site. 

 

My backup server has smaller disks than my main server. It gets backups of the unimportant  user shares. 

 

So backups are all about user shares for me and I don't have to think about disks since parity takes care of that. 

A few years back, I did a bit of statistical analysis on no parity, single parity and dual parity setups.   You can find it here:

 

       https://forums.unraid.net/topic/50504-dual-or-single-parity-its-your-choice/

 

There is also some very good discussion about hard drive failures and other considerations for data safety.   It was pointed out that dual parity actually provides additional benefits in the case where a second drive fails during the rebuild of  what was thought to be a single drive failure.  (Drive rebuilds take about two hours per TB of disk size (6TB drive will take about 12 hours)  and can be done unattended.  Data restoration usually take longer and are a much bigger hassle!)

 

EDIT:   Please notice that as the number of drives in the array increase, the chances of a drive failure really become quite significant!

Edited November 18, 20205 yr by Frank1940

what a really great thread you linked and a neat piece of analysis. Thank you for sharing it!! There was a comment about buying drives over time - my recent experience with two failed 10TB reds that failed on the same day bought on the same day from the same retailer 1.5 years ago seems too coincidental, but in a sample of 1 reinforces that comment. All the comments here strongly point to using at least one parity drive for an 8 disk array... cheers

4 hours ago, tiwing said:

what a really great thread you linked and a neat piece of analysis. Thank you for sharing it!! There was a comment about buying drives over time - my recent experience with two failed 10TB reds that failed on the same day bought on the same day from the same retailer 1.5 years ago seems too coincidental, but in a sample of 1 reinforces that comment. All the comments here strongly point to using at least one parity drive for an 8 disk array... cheers

 

That's exactly my setup. I have 4TB Parity and a Mix between 2-4TB drives in my System. Why so small? Well I build my system on a pretty strict budget and I started with the idea of I can always add another drive if I need to vs I can always buy a larger drive. Now with 8 drives in play and a SSD and a Parity I'm full on bays. So when I need more space I just upgrade a drive at a time since drives in the lower capacity have been pretty cheap. Also Id rather loose 2-4TB of data vs 10-14TB of data at a time. My thought process might not be agreeable with everybody, but so far so good. 😃

 

You could either keep your larger drive as an offsite backup and add cheaper smaller drives depending on your budget and space requirements or go big, but I tried to avoid going big simply because I'd end up spinning up larger/costlier drives than I actually needed.